Water masers accompanying OH and methanol masers in star formation regions

The ATCA has been used to measure positions with arcsecond accuracy for 379 masers at the 22-GHz transition of water. The principal observation targets were 202 OH masers of the variety associated with star formation regions (SFR)s in the Southern Galactic plane. At a second epoch, most of these targets were observed again, and new targets of methanol masers were added. Many of the water masers reported here are new discoveries. Variability in the masers is often acute, with very few features directly corresponding to those discovered two decades ago. Within our current observations, less than a year apart, spectra are often dissimilar, but positions at the later epoch, even when measured for slightly different features, mostly correspond to the detected maser site measured earlier, to within the typical extent of the whole site, of a few arcseconds. The precise water positions show that approximately 79% (160 of 202) of the OH maser sites show coincident water maser emission, the best estimate yet obtained for this statistic; however, there are many instances where additional water sites are present offset from the OH target, and consequently less than half of the water masers coincide with a 1665-MHz ground-state OH maser counterpart. We explore the differences between the velocities of peak emission from the three species (OH, methanol and water), and quantify the typically larger deviations shown by water maser peaks from systemic velocities. Clusters of two or three distinct but nearby sites, each showing one or several of the principal molecular masing transitions, are found to be common. In combination with an investigation of correlations with IR sources from the GLIMPSE catalogue, these comparative studies allow further progress in the use of the maser properties to assign relative evolutionary stages in star formation to individual sites.Comment: 51 pages, 7 figure

Surface passivation effect by fluorine plasma treatment on ZnO for efficiency and lifetime improvement of inverted polymer solar cells

Zinc oxide (ZnO) is an important material for polymer solar cells (PSCs) where the characteristics of the interface can dominate both the efficiency and lifetime of the device. In this work we study the effect of fluorine (SF6) plasma surface treatment of ZnO films on the performance of PSCs with an inverted structure. The interaction between fluorine species present in the SF6 plasma and the ZnO surface is also investigated in detail. We provide fundamental insights into the passivation effect of fluorine by analyzing our experimental results and theoretical calculations and we propose a mechanism according to which a fluorine atom substitutes an oxygen atom or occupies an oxygen vacancy site eliminating an electron trap while it may also attract hydrogen atoms thus favoring hydrogen doping. These multiple fluorine roles can reduce both the recombination losses and the electron extraction barrier at the ZnO/fullerene interface improving the selectivity of the cathode contact. Therefore, the fabricated devices using the fluorine plasma treated ZnO show high efficiency and stable characteristics, irrespective of the donor : acceptor combinations in the photoactive blend. Inverted polymer solar cells, consisting of the P3HT:PC71BM blend, exhibited increased lifetime and high power conversion efficiency (PCE) of 4.6%, while the ones with the PCDTBT:PC71BM blend exhibited a PCE of 6.9%. Our champion devices with the PTB7:PC71BM blends reached a high PCE of 8.0% and simultaneously showed exceptional environmental stability when using the fluorine passivated ZnO cathode interlayers

Dynamics of electric charge transport and determination of the percolation insulator-to-metal transition in polyvinyl-pyrrolidone/nano-graphene platelet composites

Polyvinyl-pyrrolidone loaded with different fractions of dispersed nano-graphene platelets (NGPs) were studied by Broadband Dielectric Spectroscopy in the frequency range of 1 mHz to 1 MHz. Complex permittivity and dynamic ac conductivity as a function of frequency, temperature, and composition were explored. The concentration-dependent insulator-to-conductor transition was traced through the dependence of the dc conductivity and the onset of the dispersive ac conductivity. The temperature evolution of the dielectric spectra below and above the fractional threshold exhibits different dynamics and signs the critical percolation threshold. Percolation is dictated by quantum penetration of the effective potential barrier set by the polymer matrix operating in parallel with conduction along physical contact of NGPs, in accordance with predictions for systems consisting of a semi-conducting matrix and dispersed conducting inclusions. © 2017 Author(s)

Low-cost electrodeposition of size-tunable single-crystal zno nanorods

In this paper we report a low cost, simple, electrochemical method for large-area growth of single crystal ZnO nanorods. The method utilizes a metallic zinc foil as the source of the necessary zinc ions for ZnO growth on indium-doped tin oxide (ITO) glass slides. The method is thoroughly discussed and investigated varying all the parameters involved. The resulting ZnO nanorods are highly oriented along c-axis and densely packed, while their length and diameter can be tuned by varying the growth parameters. Two different types of seed layers on the ITO glass slides are tested. A seed layer made by spin coating of ZnO nanoparticles results in a twofold increase of the ZnO nanorod surface density as compared with a ZnO thin film seed layer by physical vapor deposition. Additionally, the effect of oxygen supply during electrodeposition was investigated as a crucial regulatory parameter not only for the geometrical and topological characteristics of the ZnO nano-arrays but for their physical properties as well. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Study of the photoluminescence of N-doped, Carbon Dot-based nanocomposite materials from citric acid and urea

In this work, we investigate the photoluminescence mechanisms of N-doped, CQD-based nanocomposites, in the form of aqueous suspensions as well as the transition to thin films, in order to facilitate their use for solid-state applications. The products of two different synthetic routes have been investigated for their optical response in the form of aqueous suspensions and thin films. In addition, dialysis was utilized to purify and separate the as-synthesized material into different fractions, which were then studied separately. The PL spectra revealed two optical centers identified as H-Aggregates of citrazinic acid derivatives and 4-hydroxy-1H-pyrrolo[3,4-c]pyridine-1,3,6(2H,5H)-Trione (HPPT). The materials were further studied with FTIR and UV-Vis spectroscopy, as well as TEM microscopy, in order to acquire a better understanding of these optical centers. The optical centers were found to be excitation-independent emitters, sensitive to ambient pH conditions and able to interact with each other by an energy transfer mechanism in the solid state. © 2022 World Scientific Publishing Company

A Novel Method for the Growth of Cu2O/ZnO Heterojunctions

AbstractA novel two step electrochemical deposition method for the synthesis of ZnO/Cu2O heterojunctions is reported. ZnO nanorods were grown on seeded oxidized silicon substrates and were subsequently employed as working electrodes for the electrodeposition of Cu2O in the same aqueous formamide solution using Zn and Cu foils as counter-electrodes respectively. Single crystalline Cu2O particles grow on top of the single crystalline and vertical to the substrate ZnO nanorods. Varying the growth parameters different Cu2O morphologies can be obtained, ranging from isolated cube and truncated cube particles to a continuous layer

Positron emission tomography/computed tomography to improve staging and restaging in Merkel cell carcinoma.

8552 Background: Merkel cell carcinoma (MCC) is a rare (~1,500 cases per year) and highly aggressive (33% mortality) cutaneous neuroendocrine carcinoma that occurs in older white patients on the UV-exposed skin of the head, neck, and extremities. As a patient’s stage at presentation is a strong predictor of survival, and there is a high propensity for locoregional recurrence and distant progression, imaging remains crucial for initial and subsequent management. There is, however, no consensus on the timing or method of imaging for MCC. Methods: We retrospectively reviewed 270 2-fluoro-[18F]-deoxy-2-D-glucose (FDG) positron emission tomography/computed tomography (PET/CT) scans performed in 97 patients at the Dana-Farber/Brigham and Women’s Cancer Center from August 2003 to December 2010. Results: The mean SUVmax was 6.5 for primary tumors, 6.4 for regional lymph nodes, 7.2 for distant metastases (all sites), 8.0 for bone/bone marrow metastases, and 9.4 for non-regional metastases in those patients with no identified primary. PET/CT imaging performed for initial management tended to upstage patients with more advanced disease (50% of stage IIIB patients). Metastases to bone/bone marrow (12 patients, 38%) was the 2nd most common site of distant spread after non-regional lymph nodes (19 patients, 59%), followed by skin (8 patients, 25%), liver (6 patients, 19%), lung/pleura (5 patients, 16%), adrenal (3 patients, 9%), muscle (3 patients, 9%), pancreas (2 patients, 6%), and peritoneum (1 patient, 3%). In 10 of 12 patients, PET identified bone/bone marrow metastases that were not seen on CT imaging, which resulted in either upstaging or initiation of more targeted palliative therapy. Conclusions: Added value of PET over CT, such as in the detection of bone/bone marrow metastases, may lead to more accurate staging, and thus prognostication, as well as earlier detection of relapse and initiation of salvage treatment. Its use should be considered in the staging and restaging of MCC. </jats:p